Survival Rate and Cervical Bone Loss of Dental Implants Placed in Regenerated Areas with Free Iliac Graft

Statement of the Problem: For many years, practitioners have been encountered with dental rehabilitation of atrophic jaws. Among many of alternatives, free iliac graft can be a reasonable and also problematic choice to be accomplished. Purpose: The aim of this study was to evaluate the implant survival rate and bone loss in implants inserted in reconstructed jaws with free iliac graft. Materials and Method: In this clinical trial study, twelve patients that underwent bone reconstruction with free iliac graft were included in this retrospective study. The patients underwent surgery over a 6-year period from September 2011 to July 2017. Panoramic images were taken immediately after implant insertion and at the follow-up session. The parameters that were assessed included implant survival rate, bone level changes, and surrounding tissue conditions. Results: One hundred and nine implants were placed in eight female and four male patients, of which 65 (59.6%) were inserted in the reconstructed maxilla and 44 (40.3%) in the reconstructed mandible. The interval between the reconstruction surgery and follow-up session was 28.75 months and the mean interval between implant insertion and the follow-up session was 21.75 months, ranging from 6 to 72 months. The total average of crestal bone resorption was 2.44 mm (range: 0 to 5.43 mm). Conclusion: This study found that rehabilitation of atrophic jaws with dental implants placed in free iliac graft was associated with acceptable marginal bone loss, survival rate, satisfaction, and esthetic results among the patients.


Introduction
Many techniques have been advocated for alveolar ridge augmentation [1]. Different causes such as trauma, tooth extraction, periodontal disease and several pathological conditions lead to jaw atrophy. However, restoration of the oral function, aesthetic aspects, and mastication of atrophic jaws remain a challenge in dental implantology [1]. Resorption of jaws is lifelong, irreversible, chronic, and cumulative. The greatest amount of resorption occurs during the first year with the most rapid rate in the first three months [1]. Autogenous bone has been con-sidered as the gold standard for grafting procedures and an ideal bone substitute [2]. All three crucial characteristics, including osteoconductive, osteoinductive, and osteogenic properties are combined in autogenous bone graft with no risk of disease transmission [2].
Osteogenesis is of particular importance. It has been shown that autogenous bone grafts such as iliac crest grafts can induce osteogenesis due to a high proportion of bone marrow and human growth factors as well as a large number of living undifferentiated cells [3]. However, limitations of autografts including limited donor sites, postoperative morbidity, unpredictable resorption, complexity of the surgical procedure, and increased operation time have been debated [2].
Extraoral donor sites such as the iliac crest, tibia, or calvarium have shown acceptable potency for reconstruction of atrophic ridges, although free iliac crest graft remains the first choice due to its sufficient quantity and harvest safety [4][5]. Among extra oral donor sites, it has been postulated that iliac crest and tibial grafts have higher resorption rates as they originate from endochondral ossification [6].
Placement of osseointegrated dental implants following maxillomandibular iliac crest grafting significantly promotes all aspects of oral function in partially or completely edentulous patients [7]. Furthermore, the results have shown the low morbidity and high reliability of free iliac grafts in preprosthetic alveolar ridge rehabilitation. A few follow-up studies have evaluated the long-term outcomes of patients undergoing free iliac graft reconstruction; however, it is critical to assess the long-term clinical outcomes for a thoughtful treatment planning.
The purpose of this study was to evaluate the survival rate, success, and marginal bone loss of dental implants placed in nonvascularized iliac bone graft after reconstruction of atrophic jaws.

Results
Twelve patients including 8 females and 4 males with a mean age of 53.33 years were included in this study.
Of the 109 dental implants, 65 were inserted in the re-  Table 1). The spearman rank correlation between age and crestal bone resorption was 58.04%, which was significant except for the age group 57-63, which has been decreased ( Table 2) Satisfaction with prosthetic rehabilitation was achieved in 10 out of 12 patients, of whom 2 were not completely satisfied.

Discussion
Different factors including host defense mechanism, recipient bed, graft volume, method of protecting graft after harvesting, sufficient contact of the graft and recipient bed, and integrity of the harvested bone with the atrophic jaws can affect the resorptive process [9]. This phenomenon is inhibited by physiologic stress, stimulation, and persistent and dynamic loading of prosthetic treatment [9]. Implant insertion in the reconstructed maxilla and mandible has been advocated to decrease bone resorption. Bone resorption rates of 30-90% have  been reported after augmentation in removable denture wearers [8].
The survival rate of dental implants has been reported to be 60-70% by Keller et al. [10]. In the present study, intimate bone graft incorporation with host bone was observed in all 12 patients and the survival rate after a follow-up course (average: 21.75 months with a range of 6-72 months) was 100%, indicating that restoring all aspects of oral function in patients with atrophic jaws can be achieved by reconstruction prior to implant insertion.
In other studies, a cumulative survival rate of 97.2% was also found in patients who underwent implant placement in free iliac graft following mandible segmental resection [11]. According to a systematic review [12] and some retrospective studies [13][14][15], implant insertion in native and augmented bone is associated with equal results, which is consistent with our findings.
Nkenke et al. [16] found that although implant survival and success rates following reconstructive procedures were high, the type of implant was more important compared to the type of bone graft. However, similar to the present study, they were not able to find a significant relationship between the type of implant and cumulative success and survival rates.
The bone loss level was measured in many studies, which all found bone loss levels ranging from 0.5 to 3 mm in the first year of function. After the first year of implant insertion, the resorption rate was not significant and could be considered relatively negligible in most cases [16][17][18][19].
Quiles et al. [17] found an average bone loss of Of the different success criteria, annual vertical bone loss less than 0.2 mm is the most important one, which was observed in 77 implants in our study (70.64%). In addition, vertical bone loss less than 3 mm was found in 85 implants in the follow-up session, indicating the high success rate of this procedure. It can be construed that reconstruction of severely atrophic jaws with iliac crest free graft before implant insertion is a safe and predictable alternative. The patients regained masticatory function with acceptable aesthetic results.